1. Field of the Invention
The present invention relates generally to negative pressure wound therapy (NPWT) and in particular to dressings for surgical incisions.
2. Description of the Related Art
Current external or topical vacuum-assisted dressings (also referred to as negative pressure wound therapy (NPWT) systems (e.g., post-surgical, incisional dressing systems)) have been shown to quickly (e.g., possibly within a few hours) seal and close the dermal-epidermal portion of the skin incision (side-to-side). This has the consequence (clearly evident in several clinical studies now) of preventing surface bacteria from entering the incisional space or the wound below and thus preventing incisional or surgical wound infection, particularly superficial infection.
An area of investigation relates to the “deep” sub-dermal effects of topical vacuum-press systems and treatment procedures. For example, an investigational topic relates to the prevention or reduction of the effects of seroma and hematoma. Another area of investigation concerns how far sub-dermal or deep in the incision/surgical wound is there an effect of the dressing on the surface.
Previous systems have used rayon-wrapped Granufoam dressing material (Kinetic Concepts, Inc. of San Antonio, Tex.) and NPWT techniques on the skin surface with a liner, routinely accompanied by large dissection space procedures with deep “Hemovac-type” drains brought out through separate stab wounds peripheral to the incision. Differences in the behavior of these drains have been observed clinically compared to the drainage characteristics known to occur without the external vacuum-assisted dressing, indicating that post-incisional dressings effected outcomes. Without this vacuum-press type surface dressing, these Hemovac-type drains would have a significant measureable amount of drainage over the first few days, then decreasing to what is considered an “irritation” level of drainage (10-20 cc's of clear yellow serum—i.e., no bleeding, just the amount of reactive drainage associated with the simple presence of this plastic tube in the tissue preventing complete apposition of the tissue by its presence).
The concept is that this amount of drainage would continue day after day as long as the tube was in place. But with a NPWT type of dressing in place, drainage during the first few post-incision days can be significantly decreased—essentially to irritation levels. In fact, oozing into the drain, after closure of the incision, has sometimes been observed to suddenly stop after the foam dressing is compressed with the drains placed deeply, e.g., at fascia level. So it was felt that deep bleeding ceased when the vacuum-press dressing was compressed using NPWT procedures. These observations suggest that vacuum-press post-operative dressings decrease hematoma and seroma formation.
As an incision is being closed, tissue voids, pockets, spaces and irregularities may prevent firm tissue-to-tissue apposition and create an actual “space.” This is quickly filled by fluid—depending on the circumstances, this fluid consists of a spectrum from pure blood to pure extracellular and lymph fluid without any blood or serum clotting factors. The initial behavior of this fluid collection depends on which side of the spectrum it is. If there is enough pure blood to clot, this will be a hematoma. The consequence of any “space-occupying” hematoma is that the process of clot lysis, which proceeds over several days, carries with it the risk of “unclotting” blood vessels of sufficient size and pressure such that rebleeding occurs and causes a post-operative complication of an “expanding hematoma.”
If re-bleeding does not occur, problems can occur with probable expansion at both ends of this spectrum of fluid in a space. Lysis, cell and clot breakdown with the freeing of protein can all produce particles that create an osmotic pressure. If this is greater than the absorptive capability, the fluid expands rather than contracts. If that occurs early before there is any collagen production with strength, then this breaks apart the surrounding tissue apposition (aided by any irregular tension from the suture position, necrosis from just the presence and nature of the suture ligatures, cautery debris, surface of the incision trauma from the very act of surgery, etc.). In other words, one can think of the dissection space of an operation as easier to be again split apart than to be held together.
So, even in a relatively pure seroma that never had any significant amount of blood in it to start with, there is still enough oncotic pressure from the unabsorbed large proteins such that expansion becomes a greater force than absorption and that, plus the simple mechanics of the presence of liquid between layers preventing collagen bridging and development of any strength between opposing layers of tissue, allows us to see that seromas also “expand” and we can see how just their very presence is a potentiating factor for “dehiscence.”
If we look at the above scenarios, we get another glimpse at what NPWT-incisional dressings or topical vacuum pack dressings systems seem to be doing: they are changing the healing process during the critical first 48 hours of wound healing. Because the dressing enhances and enables tissue apposition, not only at the surface but also at levels beneath the dressing, it reduces and prevents the early increase in size of liquid-filled space lesions in incisions. But a review of the current data suggests that it does not take away a space-occupying fluid collection that is already there on completion of the closure before a NPWT-incisional dressing is applied, e.g., in the operating room. Use of a buried suction drain such as a Hemovac drain may reduce this. But looking at these dynamics in this way suggests another alternative.
If we look at methods to decrease the presence of liquid-filled space-occupying lesions (i.e. hematoma/seroma) at the moment the incision is compressed on the operating table, we see an alternative to Hemovac drains brought out through a separate stab wound and left for several days, and to the option of preventing complete sealing of the incision by placing Swanson-type or wick drains through the incision, at its end or between sutures and leaving them for 24 to 72 hours to allow the incision to drain, and then having to change the entire topical vacuum-pack system, and that alternative is to drain the hematoma/seroma collections that form during closure on the operating table just before or, preferably, just after the foam core in the external dressing is compressed and then remove the drain and seal the dressing before the patient leaves the operating room.
Again, this entire concept can be summarized by the idea of the “set” of the wound or incision. Orthopedic surgeons reduce and hold fractures in position as the plaster cast is applied. Plastic surgeons roll and “milk” wounds to get everything drained and in a suspended new position before the wrap or tape or garment is applied to hold this “set.” General surgeons use “retention” sutures and large ligatures to hold at-risk abdominal incision closures in place.
External vacuum-assisted NPWT systems use dressings that are eminently suited to hold the tissues in set apposition. The task then is to formalize the final removal of still-present drainage and to arrange the set of the wound as the foam core compresses. This disclosure then is to propose alternative methods and materials to accomplish that for both the peel-and-place and the customizable NPWT systems.